This invention relates to the field of waste disposal, and in particular to disposal of aerosol spray containers and the contents thereof in an economical and environmentally responsible manner.
Aerosol spray containers, such as spray cans and bottles, have long been employed primarily for delivery of liquid materials in the form of a mist or foam. Typically, the aerosol delivery systems employ one or more propellants, at least one of which has a substantial vapor pressure at room temperature. The propellant or propellant mixture which powers the aerosol exists in the pressurized atmosphere of the charged aerosol, at room temperature, in a liquefied physical state, although the headspace contains some gaseous propellant(s).
Aerosol filling plants generally operate on industry-standardized propellant specifications. Product manufacturers commonly fill their own aerosols; an equally common practice is that a product as formulated by the manufacturer is shipped to an aerosol filling operation as an unpressurized bulk or containerized liquid and filled to the product manufacturer's specifications. The particular propellant composition employed is determined in large part by the physical characteristics of the particular product; in general, a central requirement is the ability to attain a specific fill vapor pressure specified by the product manufacturer.
Although a wide range of materials are dispensed in aerosol containers over a range of vapor pressures, there are only a limited number of propellants in general use. The attainment of the necessary range of vapor pressures is achieved by blending a relatively low number of actual propellant materials, with a range of variations in the proportions of the components and the amount of the propellant mixture in the delivery vehicle.
It should be noted that different products dampen or decrease the internal vapor pressure of the product loaded aerosol to different degrees. Thus, two different products, both of which require a charged pressure of e.g. 70 psi and both of which require charging with identical propellants, may require charging of the identical propellants in different proportions.
The propellants in general use at this time include low molecular weight hydrocarbons, such as dimethyl ether (oxygenated), propane, butane and isobutane; the chlorofluorocarbons, such as the various materials commercially available under the designation Dymel or Freon; and inert propellants, such as carbon dioxide, nitrogen and nitrous oxide. Mixtures of propellants within a group, as well as from different groups, are most commonly employed to achieve the desired vapor pressure.
The hydrocarbon group of propellants is one of the two most commonly employed groups and comprises methane, ethane, propane, n-butane, isobutane and dimethyl ether. Mixtures of these hydrocarbons are generally employed to attain different pressures. The actual mixtures employed are usually industry standardized and coded by reference to the maximum pressure attainable therewith; pure propane may be used to achieve a pressure of about 108 psi.
The chlorofluorocarbon group is currently the other most commonly employed group of propellants. It comprises the various chlorofluorocarbons, commercially marketed under a proprietary name such as Freon or Dymel, followed by a numerical designation identifying the particular chlorofluorocarbon compound. The industry also commonly substitutes the chlorofluorocarbon proprietary name with a "P" followed by the identical numerical designation to identify a particular chlorofluorocarbon compound. Due to damage to the ozone layer, the use of these chlorofluorocarbons will be phased out over the next ten years. Mixtures of the chlorofluorocarbons are employed for non-flammable uses; in addition, they may be mixed with hydrocarbons and/or other propellants to attain desired specifications.
Dimethyl ether is achieving more widespread use as the chlorofluorocarbons are being phased out. Dimethyl ether is very volatile and potentially explosive; therefore, it is usually cooled by use with aqueous products or by blending with the nonflammable chlorofluorocarbons.
Finally, the group of inert propellants comprises carbon dioxide, nitrogen and argon; of these, only the first two are generally employed to any significant extent. Carbon dioxide is normally used with solvent based products. Nitrogen is often used to propel products which contain ingredients requiring a relatively high vapor pressure which cannot be attained with the other propellants in use.
Of the aerosol products currently available, less than about 20% employ inert propellants. The vast majority of aerosols are propelled using hydrocarbons, chlorofluorocarbons or mixtures thereof. Under current usage, the hydrocarbon group probably enjoys a slight edge over the chlorofluorocarbons; however, as the use of the latter class is discontinued, it is anticipated that the use of dimethyl ether will increase.
Recent changes in federal regulations have made it not longer possible in most instances to dispose of unpunctured aerosol containers in simple landfills. While unpunctured aerosols may be fed into licensed incinerators at a controlled rate, incinerator time is expensive and regulatory problems may be encountered due to the quality of the resultant flue gas (in particular, with respect to CO emissions). Moreover, while the chlorine content of the flue gas may be accommodated by scrubbing, this is not the case with respect to fluorine, and there is the added disadvantage that fluorine may react with the brick lining of the incinerator. Local air quality regulations often prohibit venting of the residual content of aerosol containers to the atmosphere, and uncontrolled release of chlorofluorocarbons to the atmosphere would in any event be undesirable in view of potential long-term consequences to the environment. In short, there is clearly a need for alternative methods for the safe and economical disposal of aerosol containers and the residual contents thereof.
It is an object of the present invention to provide a method whereby disposal of aerosol spray containers is facilitated. In particular, it is an object of the invention to eliminate the risk of explosion associated with the puncturing of aerosol spray containers, while preventing the escape of deleterious propellant materials into the atmosphere. In addition, it is desired that recovery and disposal of the residual contents of an aerosol spray container in addition to the propellant be possible in a simple and efficient manner.